Lockbox post processing in SAP for Partially Applied/on account & unprocessed status

does anyone know the exact steps involved in lockbox post-processing for three status as mentioned on the subject?a comprehensive answer is much appreciated

1. Partially Applied - steps involved after selecting the check and the posting directs you to basic incoming payment clearing screen so what posting keys and document types should be selected in this instance? since the check has already been partially applied does this mean unapplied invoice(s) have to be selected from "process open Items"?

2. on Account - what is the initial step involved? should this be initiated through editing payment advice and incorporating manually the customer code with the background check and post it using the standard approach as point 1

3. unprocessed checks - does the first action should be by editing the payment advice and following point 2?

thanks in advance